1. Field of the Invention
This invention relates to a rotor for an electrical machine.
2. Description of the Related Art
Electrical machines (generators and motors) typically contain a rotating member called a rotor. Referring to FIG. 1, a rotor typically is comprised of pole pieces 11 and an electric coil assembly 12. Pole pieces 11 illustrated in FIG. 1 are from a "claw pole" rotor, a typical rotor found in alternators used in automobiles. Coil assembly 12 comprises wire wound around a bobbin. Typically, when the machine is operating, the wire is energized to create a magnetic field. The magnetic field in turn magnetizes pole pieces 11, creating magnetic poles at the claws of pole pieces 11. Those magnetic poles then play their part, as is well-known in the art, when the alternator generates electrical power.
Because a rotor in an electrical machine rotates, coil assembly 12 needs to be affixed to pole pieces 11 to assure that coil assembly 12 rotates along with pole pieces 11 in the rotor. Furthermore, the wire of coil assembly 12 must be affixed to the bobbin, to assure that the wire does not rotate or otherwise move with respect to the bobbin. Relative movement between the wire and the bobbin as the rotor rotates can cause premature failure of the wire.
A typical way of affixing coil assembly 12 to pole pieces 11 is through the use of an adhesive such as epoxy. The adhesive holds coil assembly 12 to pole pieces 11. One typical way of bonding the wire of coil assembly 12 to the bobbin is through the use of varnish applied to the wire after it is wound on the bobbin. However, because varnish does not stick well to typical bobbins, varnish alone provides only marginal adhesion. A second way of bonding the wire of coil assembly 12 to the bobbin is through adhesive-impregnated tape wrapped on the bobbin before the wire is wound, or on the coil after the wire is wound. The coil is then typically heated to melt the adhesive on the tape. However, the coating of some of the wires of the coil assembly is often less than perfect when such tape is used. Relative movement of some of the wires, and a consequent decrease in durability of the alternator, can then result. A third way of bonding the wire of coil assembly 12 to the bobbin is through holes in the side walls of the bobbin. When the bobbin is adhesively bonded to the pole pieces 11, some of the adhesive flows through the holes, bonding the wire to itself and to the bobbin.
Although adhesives are often effective in affixing the various parts described herein, there are some disadvantages to the use of such adhesives. The processes by which the adhesives are applied add complexity to the manufacture of an alternator. The processes further often require expensive equipment. Additionally, some of the aforementioned methods of adhesively bonding wires to the bobbin do not provide bonding with very high reliability.
U.S. Pat. Nos. 3,305,740 and 4,307,314 provide non-adhesive ways to hold a coil assembly to a pole piece. However, neither of those patents addresses the issue of affixing coil wire to a bobbin in other than the prior-art ways of doing so. Furthermore, the ways provided by those patents to hold a coil assembly to a pole piece are relatively difficult to manufacture.
Therefore, an invention which provides easy-to-manufacture means for affixing a coil assembly to pole pieces without adhesives and which provides means for affixing coil wire to a bobbin with high reliability and with reduced dependence on adhesives will provide an advantage over the prior art.